Occupationally related low back disorders (LBDs) are currently and have been the leading cause of lost work days as well as the most costly occupational safety and health problem facing industry today. It is also well known that most occupationally-related LBD is associated with manual materials handling (MMH) tasks. However, a major limitation in controlling the incidence of occupationally-related LBDs is that we have been unable to accurately assess the loading that occurs on the lumbar spine (the most common site of injury) during realistic actual whole-body free-dynamic MMH conditions so that these loadings can be compared to spine tissue tolerances. The long term objective of this work is to develop a means to accurately assess loads imposed upon the lumbar spine during actual workplace MMH conditions. A free-dynamic three-dimensional biodynamic model of the spine has been under development in the Biodynamics Laboratory at the Ohio State University for the past 12 years. The model accounts for the collective co-active influence of 10 trunk muscles upon the three-dimensional loading of the spine. The investigators have developed this model to the point where they can accurately predict three-dimensional loadings of the spine under free- dynamic bending and twisting of the lumbar spine. However, this model currently requires that the subject be confined to a pelvic restraint system so that only motion of the spine above the pelvis is permitted. Motion of the pelvis will affect the length and velocity characteristics of the trunk muscles. Thus, although promising, the model is not currently applicable to most industrial MMH tasks. The immediate goal of this effort is to further develop this biodynamic model so that it can be used to accurately assess spine loading during whole-body free- dynamic (unrestrained) lifting activities. This goal will be accomplished via three specific aims consisting of: 1) determine how the biodynamic model must be changed once the lower body is permitted to move during the lift, 2)develop instrumentation that is necessary to adjust the model appropriately for body posture changes that occur during whole body free-dynamic lifting, and 3) validate the model. The model resulting from this effort will permit the accurate assessment of biomechanical risk of LBD associated with MMH. In addition, since this model is subject specific, it will facilitate research into the biomechanical effects of psychosocial, work schedule, work rotation, and other work organizational issues.